The technical field of this invention is phototherapy and, in particular, methods and devices which employ optical fibers and other flexible light waveguides to deliver radiation to a target site.
Fiber optic phototherapy is a increasing popular modality for the diagnosis and/or treatment of a wide variety of diseases. For example, in surgery, infrared laser radiation will often be delivered to a surgical site via a hand-held instrument incorporating an optically transmissive fiber in order to coagulate blood or cauterize tissue. Similar fiber optic delivery systems have been proposed for endoscopic or catheter-based instruments to deliver therapeutic radiation to a body lumen or cavity. U.S. Pat. No. 4,336,809 (Clark) and U.S. Reissue Pat. No. RE 34,544 (Spears) disclose that hematoporphyrin dyes and the like selectively accumulate in tumorous tissue and such accumulations can be detected by a characteristic fluorescence under irradiation with blue light. These patents further teach that cancerous tissue that has taken up the dye can be preferentially destroyed by radiation (typically high intensity red light) that is absorbed by the dye molecules during phototherapy.
Others have proposed the use of fiber-delivered radiation to treat artherosclerotic disease. For example, U.S. Pat. No. 4,878,492 (Sinofsky et al.) discloses the used of infrared radiation to heat blood vessel walls during balloon angioplasty in order to fuse the endothelial lining of the blood vessel and seal the surface. Another application of fiber-delivered radiation is disclosed in U.S. Pat. No. 5,053,033 (Clarke) which teaches that restenosis following angioplasty can be inhibited by application of UV radiation to the angioplasty site to kill smooth muscle cells which would otherwise proliferate in response to angioplasty-induced injuries to blood vessel walls.
Nonetheless, a number of problems limit the expanded use of fiber-optic phototherapy. Typically, an optical fiber emits light from only its end face. Thus, the emitted light tends to be at best divergent in a conical pattern and, therefore, exposes only a small region directly in from of the fiber's distal end. The small exposure area increases the power density at the fiber tip, thus limiting the power available for phototherapy since overheating of the target tissue must often be avoided.
Although "sideways-emitting" fibers have been proposed to permit greater flexibility in phototherapy, this approach still does not allow uniform irradiation of large volumes of tissue and can also be ill-suited for applications where circumferential uniformity is desired. Because sideways-emitting fibers expose limited regions, they do little to alleviate the problem of "hot spots" which limit the intensity of radiation which can be delivered via the fiber to the treatment site.
Others have proposed diffusive tips for optical fibers to enlarge the region which can be irradiated and/or reduce the potential for overexposure. However, diffusive tips have not been satisfactory for many therapeutic purposes because of their complexity of manufacture and/or because the radiation may not be scattered uniformly enough to alleviate the problem of "hot spots." Prior art diffusive tip structures have not be capable of delivering high power radiation, e.g., on the order of ten watts or more, to facilitate photocoagulation therapy or the like.
The use of diffusive tips in phototherapy is also limited by the amount of radiation that can be transmitted through a single diffuser assembly which is typically located at the distal end of an instrument. The diffuser structures are typically cylindrical or spherical in shape to facilitate a broadly-cast exposure pattern.
Accordingly, there exists a need for better apparatus for fiber optic phototherapy. In particular, diffusive tip assemblies which could provide broadly-cast exposure patterns in radial direction (e.g., sideways) relative to the instrument axis without hot spots would satisfy a long-felt need in the art. Moreover, light diffusing assemblies that could deliver greater amounts of energy in diffuse patterns would meet a particularly important need in the field of minimally-invasive phototherapeutic surgery.